1. Field Of The Invention
The present invention relates to a fiber-reinforced piston ring for an internal combustion engine.
2. Description Of The Prior Art
Piston rings are conventionally formed of an iron-base material such a cast iron, a spring steel or a stainless steel. The recent trend in internal combustion engines is to increase the speed of rotation and the output, whereby a further reduction in the size of a piston ring is desirable in view of the increased speed of rotation while an increase in rigidity is desirable for the piston ring to accommodate the increase in output.
However, prior art piston rings have the problem of a large inertial mass because of their high specific gravities (7.0 to 7.9). As a result, when the piston speed is increased with an increase in the speed of rotation of the engine, the pressure of a combustion gas is balanced with the inertial force of the piston ring, causing a so-called fluttering which results in a condition wherein the piston ring is floating without contacting the inner opposed wall surfaces of the piston ring groove, whereby the sealing effect is reduced and causes an increase in the amount of gas blow-by.
One attempted solution to this problem has been to reduce the width (axial width) of the piston ring of an iron-based material. However this results in a problem of buckling and undulation of the piston ring by the increased pressure of the combustion gas caused by the increase in output of the engine, because the thin piston ring is less rigid than prior conventional piston rings.